Hostile environments found in deep, high pressure gas wells require that extra precaution be taken to select tubing that will last for the designed productive and shut in life of the well. These considerations often result in the selection of expensive tubing material, such as a corrosion resistant alloy (CRA). Use of the alloy prevents the premature failure of the production tubing due to the severe corrosive action that might result from the use of more common carbon steels.
The rise in popularity of CRA tubing in the 1980's generated a demand for sophisticated handling equipment and running procedures to lengthen the life span of the premium tubulars and the premium connections, or collars, that join them. Given the high cost of CRA or the like material, it was recognized that substantial savings would be reaped from utilizing lighter wall tubulars and connections. Thus, the high cost of premium material provided a strong incentive to optimize the tubing wall thickness to that that was required by well conditions alone, with the appropriate safety factor.
This invention responded to the challenge to develop non-abrasive tubing running procedures. "Non-abrasive" implies in this context that the procedure does not require increasing the thickness of the walls of the tubulars or their connections to take into account abrasion, such as die marks, incurred during running. In particular, this invention responded to the challenge to develop a procedure capable of running a 25,000 foot CRA string without tong, slip, or elevator marks.
Traditional tubing running procedures utilize elevators and slips that grip the string by exerting abrasive, radially inward pressure. These slips contain inserts that penetrate the tubing wall upon the application of the radial pressure. While the penetration ensures a firm grip for the elevator or slip, the penetration has been found to extend to a depth of 0.030 inches or greater into the outer tubing wall. The depth of the penetration increases with the depth of the well and the weight of the tubing string being supported. Assuming traditional tubing running procedures, once the tubing wall is optimized for well conditions, an additional wall thickness of at least 0.030" is required to compensate for the die penetration marks resulting from traditional running techniques. This extra wall thickness can add substantially to the cost of the tubing. As an example, on a 25,800' completion, an additional 14,000 pounds of CRA material would be required. This might add an incremental cost of $200,000 to the well.
A dual elevator running technique existed in the art in conjunction with the running of "upset" tubing. By this procedure, the load of the string is borne by the sloping shoulder of the "upset" portion of the tubular when gripped by one of a pair of elevators. The surface of the "upset," however, is abraded in this technique. Further, crevice corrosion develops in an area of stress concentration where the "upset" portion joins the tubing portion of the tubular. The walls on the "upset" portion of the tubing also are significantly wider than is required by well conditions alone. The close tolerances involved in working with the narrow faces on premium connections, whose wall thickness is designed for well conditions alone, made the use of the dual elevators technique unworkable. The mechanical play and the tolerance of the elevator latch and hinge alone was too great.
The narrow face of the premium connection discussed herein is measured by the difference between the collar's outside diameter (OD) and the collar's inside diameter (ID). For premium connections designed, together with their tubulars, to a thickness no greater than that required by well conditions, this wall thickness is not expected to be greater than 20% of the collar ID. Frequently, the width of this face is less than 10% of the ID. For instance, the premium connection for a three and a half inch CRA tubular would likely have a face width of from 0.1 to 0.45 inches, depending upon the design depth of the well and the designed location of the connection within the string. It should be appreciated that the width of the face is limited not only by cost considerations but also by the necessity that the collar's wall thickness remain compatible with the tubing wall thickness in important structural characteristics. For instance, having a collar with a wall thickness significantly greater than the tubing could cause the coupling joint to lose its seal under the stress of production in harsh environments. Under tension, the uneven thicknesses of the connection and the tubing could elongate at different rates. Within the limitations imposed on the collar thickness by the tubular's thickness, therefore, there is only slight leeway to increase the width of a collar face for running procedure purposes. Upper collars in the string that bear more weight may have only very slightly larger face widths than lower collars.
The tubing running procedure of the present invention teaches the elimination of abrasion or die penetration marks that have historically been associated with the makeup of the tubular connections. The data and performance of the present procedure has been tested, and the tests demonstrate the procedure's feasibility. Cost savings can be realized by the design of the wall thickness of premium tubulars and connections using criteria based only on well environment conditions.